In the production process of an oil-gas well, due to such causes as non-homogenous characteristics of an oil reservoir, both a vertical well and a horizontal well require packing off the oil-gas well into multiple relatively independent regions for production. The oil-gas well production here includes fluid output and injection in the production process of an oil-gas well, such as oil exploitation, or such operations as performing acidification by injecting acid fluid into the formation through an oil-gas well.
The production by packing off an oil-gas well into multiple relatively independent regions usually uses packers to separate a production section of an oil-gas well into independent flow units along the axis of an oil-gas well, each of the flow units being installed with a device for flow control. For example, the device for flow control may be a flow-control filter or the like.
Having been long dedicated to research on flow control and packing off in a production section of an oil-gas well, the applicant has discovered many problems existing in the use of a packer. The applicant applied for a patent for invention, Application No. 02158107.X filed on Dec. 23, 2002, the invention title of which is “COMPLETION SYSTEM OF OIL AND GAS WELLS WITH REGULATABLY CONTROLLING FLOWS OF FORMATION FLUID OR FILLED FLUID IN SUB-DIVIDED SECTIONS” (explanation: the patent applicant is Beijing Hinen-Hitech Petroleum Technology Development Co., Ltd, which company at present has been incorporated into ANTON OILFIELD SERVICES (GROUP) LTD.). The patent application analyzes defects of traditional packers in detail and, on such basis, discloses a completion system of oil and gas wells with regulatably controlling flows of formation fluid or injection fluid in sub-divided sections. The completion system at least includes a flow control string and a porous medium inside an oil-gas well, wherein the flow control string is a filter having a flow regulating and controlling device. The porous medium is provided in an annular space formed by the outer wall of the flow control string and the borehole wall. The flow control filter is provided with flow collecting holes and a flow collecting cavity (the flow collecting cavity is also called as a flow diverting layer) inside which the flow collecting holes are disposed for flowing of a formation fluid or injection fluid inside and outside the flow control filter. A flow regulating and controlling device is provided inside the flow collecting hole for regulating and controlling passage of a formation fluid or injection fluid through the flow collecting hole. The invention is used to regulate and control flow states of fixed sections at different positions of an oil reservoir. Compared with traditional packers, the number of pack-off sections may be increased significantly, with the pack-off sections being divided. The control precision of such downhole productions are improved for layered injection and production, testing, plugging and profile modification. In particular, the invention is adapted to development of a non-homogenous reservoir or a multilayer oil reservoir and other circumstances requiring sub-division of downhole sections for flow regulation and control.
The porous medium of the patent application, which is filled in a space between the flow control filter and the borehole wall, produces the anti-channeling effect of fluid in an axial direction, thereby in other words producing a pack-off effect to a certain extent, i.e. the porous medium is the anti-channeling pack-off particles used in a production section of an oil-gas well set forth by us at present.
The patent application further discloses that the porous medium is a loose medium, a non-loose porous medium or a combination thereof. The loose medium is formed by piling formation sands, gravel particles, ceramsites, plastic particles or a combination thereof. The non-loose porous medium is a fiber, a particle cementation, a consolidated porous cement, a porous plastic or a cementation medium formed by a combination thereof. The porous medium has a permeability rate of 300 μm2-10−5 μm2.
As a matter of fact, the patent application only puts forward a conceptual solution for selection of a porous medium but fails to take a specific option, and such can also be seen from three embodiments of the patent. Especially, although the patent application mentions that plastic particles and porous plastics may serve as a porous medium, because of various categories of plastics and significant differences in their properties, the patent application fails to mention whether the plastics machining process can satisfy the requirements of an oil-gas well for the anti-channeling pack-off particles used in a production section, and the like.
The applicant applied for a new patent application, Application No. 200810118109.X filed on Aug. 12, 2008, the title of which is “HORIZONTAL PRODUCTION-INJECTION WELL COMPLETION STRUCTURE POSSESSING FLOW CONTROL FUNCTION”. The patent application summarizes the experiments carried out by the applicant from the year of 2002 to 2008, and analyzes defects of an annular packer in the prior horizontal wells and the defects of taking sand or ceramsites as an anti-channeling pack-off medium in detail as follows: Because sand or ceramsites have a high density, due to a flow limiting effect of the flow-controlling device in a horizontal production-injection well, there are problems of small filling flow, difficulty of sand or ceramsites filling, and loose filling, thus making it impossible to achieve the purpose of preventing axial channeling of water or gas.
The patent application discloses a completion structure of a horizontal injection-production well with flow control function. The structure is comprises a borehole wall and a flow control filter. The borehole wall includes a vertical section and a horizontal section, with the flow control filter being located in a horizontal section of the borehole wall and being fixedly connected with the borehole wall. A cavity between the flow control filter and the borehole wall is filled with glassy hollow particles. The glassy hollow particles as defined in the patent application are anti-channeling pack-off media for use in an oil-gas well, and the patent further discloses that the glassy hollow particles have a compaction percentage of 80% to 100%. The glassy hollow particles are hollow beads in coal ash formed after burning or artificial hollow glassy balls. The glassy hollow particles have a density of 0.5-1.8 g/cm3. The glassy hollow particles have a particle diameter of 30 μm-1000 μm.
As the anti-channeling pack-off particles have high requirements for the density and particle diameter, the cost of the artificial hollow glassy balls is so high that it is difficult to be applied in practice. Consequently, the present applicant has sequentially carried out a quantity of experiments on using hollow beads in coal ash as a pack-off medium, through which experiments it was discovered that there still exists the following problems when hollow beads in coal ash are used as the pack-off medium:
1. The hollow beads have an actual density of mostly about 0.6 g/cm3, which has a difference of about 0.4 from the density of water at 1 g/cm3. As the flow control filter limits the flow to such a small amount to cause the pressure of water stream carrying the hollow bead to be too weak, it is still impossible to satisfy the requirements of filling up with hollow beads in most cases.
2. The hollow beads have such a poor pressure resistance that about 50% of the hollow beads will be broken when pressurized. Also, the specific gravity of the broken hollow bead is significantly increased so that such broken hollow bead may severely affect the anti-channeling pack-off effect in a production section of an oil-gas well.
3. If the pressure resistance of a hollow bead is required to reach the requirements, the particle diameter of the hollow bead will be too small to be found in reality and thus it is difficult to satisfy the requirements in most cases.
To validate the aforementioned solution, the applicant has established an appropriate experimental apparatus and uses many media to carry out a experiment for filling and packing off, for instance using quartz sand and the like to carry out a experiment for filling and packing off. In the experimental process, the applicant discovered that, due to a flow limiting effect of a flow control device, such particles as quartz sand are filled so loose as to form a major vacancy and channeling.
A desirable material is required to withstand the downhole high temperature, high pressure and high strength extrusion force. A desirable material is further required to be resistant to oil and water, in many circumstances is also required to be resistant to strong acid, and moreover is additionally required to be stable over several years or a decade. Moreover, it is also necessary for the materials to have a particle diameter in order to achieve the requirements. Over many years, the applicant has long endeavored persistently with experiments to prove that most plastics do not satisfy the requirements of an oil-gas well for anti-channeling pack-off medium.
Owing to the production characteristics, an oil-gas well has other strict requirements for a pack-off medium. On the one hand, the pack-off medium should not plug an oil-gas well; otherwise, it may cause the oil-gas well to be discarded due to no production-fluid. On the other hand, the permeability of the pack-off medium should be neither too high nor too low, such that it is possible to reach a small radial resistance and a large axial resistance so as to achieve the purpose of blocking an axial flow of formation fluid or injection fluid in the oil-gas well, and at the same time allowing a radial penetration of formation fluid or injection fluid in an oil-gas well. Such requirements necessitate the particle diameter to be within a required range.